In typical printers, integrated circuits or chips are provided on printheads for performing signal processing. Usually, these chips interpret serial data streams containing encoded data for controlling the printing operation, such as the production of a printed image or data, and control of the printhead itself. The types of signals provided to the chip on the printhead would include logic, power, a clear signal, clock signals, such as CLOCK and LOAD, and data signals corresponding to the image or data to be printed. The need to provide numerous signals to the printhead increases the cost of the printer because it requires a large TAB circuit. The TAB circuit provides an interconnection between the printer and printhead, and usually a separate line is required for each type of different signal that is applied to the printhead. Thus, reducing the number of lines in a TAB circuit will significantly reduce the cost of the printer and the printhead.
Another significant factor in the cost of the chip is the size of the chip, and the size of the chip usually goes up in proportion to the number of signals and the types of signals that the chip must interpret. Increasing the size of a chip usually increases its cost.
The present invention reduces the cost of the the printhead by reducing the number of lines in the tab circuit and by reducing the overall size of the circuits required on the tab circuit.
In accordance with one embodiment of the present invention a printhead is provided for use in an inkjet printer in which printer electronics produce logic signals and apply the logic signals to the printhead through an interconnecting circuit. The printhead includes a plurality of nozzles for directing ink out of the printhead, and a plurality of ejector mechanisms that force ink through the nozzles. A printhead power circuit directs power to the ejector mechanisms and a logic power supply is connected to receive at least one logic signal from the interconnecting circuit. The logic power supply derives a power signal from the logic signal and supplies the power signal to a logic circuit. Thus, the logic circuit receives a power signal without having a dedicated logic power line in the interconnecting circuit between the printer electronics and the printhead.
The logic power supply circuit may be a single isolation device connected to a single logic signal. However, it is preferred that the logic power supply circuit be connected to at least two different logic signals and, thus, the logic power supply circuit may comprise two diodes or other electronic isolation devices. The electronic isolation devices, such as diodes, derive power from the logic signals and apply that power to the logic circuit, but the isolation devices also isolate the logic circuit from the logic signals so that power cannot flow in a reverse direction from the logic circuit to the interconnecting circuit or other lines that carry the logic signals.
In a particular embodiment, the logic power supply circuit is part of an electrostatic discharge protection circuit that is connected to a logic signal and to the logic power supply circuit. The electrostatic discharge protection circuit is configured to derive the logic power signal from logic signal and apply the logic power signal to the logic circuit of printhead. The electrostatic discharge protection circuit includes an electronic isolation device, such as a diode, that performs a dual function. It helps protect the circuit against electrostatic discharge, and it derives power from the logic signals and applies that power to logic circuit while simultaneously isolating the logic circuit from logic signals. The term “isolating” in this context means that the isolation device prevents reverse current flow from the logic circuit back to the lines carrying the logic signals, but it allows forward current flow.
In accordance with a method of the present invention, power is provided from one portion of a printer, such as a printer electronics module, to another portion of the printer, such as a printhead. Logic signals are produced in a first electronic module of the printer and are transmitted by an interconnecting circuit to a second electronic module of the printer. A logic power signal is derived from the logic signals without interfering with the magnitude or duration of logic signals, and the logic power signal is applied to power the second electronic module without having a separate dedicated power line in the interconnecting circuit to power the second electronic module. The method may be implemented by deriving a power signal from a single logic signal, but it is preferred that the method be implemented by deriving of the power signal from multiple logic signals, where at least one of the logic signals is active (high) at any point in time. In one embodiment the method is performed by electronic isolation devices that are already present in the printhead performing other functions. For example, the method may be performed by electronic isolation devices that are already present in an electrostatic discharge protection circuit in the printhead. The electronic isolation devices derive a logic power signal from the logic signals while simultaneously providing electrostatic discharge protection. Thus, the method may be implemented with little or no additional cost in the second electronic module of the printer because an isolation device that is already present in the second electronic module is being reconfigured to perform dual functions without sacrificing its original function. For example, two diodes that are already present in an electrostatic discharge protection circuit may be connected to derive the logic power signal from the logic signals without adding any new devices to the second electronics module.